Regulatory mechanisms underlying florigenesis in Vanilla planifolia Andrews: A study of MADS-box gene family

Orchid flowers have unique floral organisation which make them indispensable to the floral industry. The MADS-box gene family encodes for transcription factors that are involved mainly in floral organisation. This study was conducted on Vanilla planifolia, which is an important orchid that is commercially exploited by the food industry for a highly valued flavour, vanillin. V. planifolia transcriptome was analysed and 33 MADS-box transcripts that encode putative MADS-box proteins, were identified. Phylogenetic analysis of the VpMADS proteins with other closely related plant species showed clear clustering into type I and type II. Protein characterisation, duplication events, and their evolutionary analysis were performed. The spatio-temporal expression profile for VpMADS genes at different plant developmental stages showed high expression of these genes in specific floral tissues. Secondary and tertiary structural analyses was also done for 13 MADS-box proteins representing each sub-class and their 3D structures were deduced. This study provides a basic understanding of the functioning of MADS-box gene family in V. planifolia and paves the path for functional characterisation of selected VpMADS genes in planta and in a heterologous system for managing the commercially important traits in this orchid.兰科植物具有独特的花部结构，这使其在花卉产业中具备不可替代的产业价值。MADS-box基因家族（MADS-box gene family）编码的转录因子主要参与花部发育调控。本研究以食品工业中因高价值香兰素（vanillin）而被商业化开发的重要兰科植物香荚兰（Vanilla planifolia）为实验材料。对香荚兰的转录组进行分析后，共鉴定得到33个编码推定MADS-box蛋白的MADS-box转录本。将VpMADS蛋白与其他近缘植物物种开展系统发育聚类分析，结果显示其可清晰划分为I型和II型两类。本研究同时完成了蛋白特征解析、基因复制事件分析以及进化分析。针对不同植物发育阶段的VpMADS基因进行时空表达谱分析发现，该类基因在特定花组织中呈现高表达水平。此外，针对覆盖每个亚类的13个MADS-box蛋白完成了二级与三级结构分析，并推导得到其三维空间结构。本研究为解析香荚兰中MADS-box基因家族的功能机制提供了基础认知，同时为后续在植物体内及异源表达系统中对筛选获得的VpMADS基因开展功能鉴定，以改良该兰科植物的重要经济性状铺平了研究路径。